1. Field of the Invention
The present invention relates to petroleum refining plants. More specifically, the present invention relates to method of cleaning and maintaining a petroleum refining plant, in which process equipment such as a furnace, reactor, heat exchanger and stripper are chemically cleaned, and rinsed after a softening catalyst agglomerated in the reactor and a surface of the catalyst softened by the chemical cleaning is coated and passivated, these processes being combined and conducted simultaneously.
2. Description of Related of Related Art
Crude oil is refined and various products and feed materials for chemical petroleum plant are manufactured in a petroleum refining plant, in which various catalysts are used. Catalayst activity deteriorates during continuous plants operation due to coking, poisoning or the like. Accordingly, periods repair to exchange the catalyst is necessary. The catalyst is exchanged by initially unloading the spent catalyst and subsequent loading of new catalyst.
The catalyst is mainly exposed to a reducing atmosphere during operation of the aforesaid petroleum refining plant. Therefore, when thus reduced catalyst is exposed to the air for replacement, the catalyst is oxidized to generate heat, thus causing possible ignition of carbide, sulfur and the like adhered to the catalyst during operation.
Therefore, after the catalyst beds are cooled from a high temperature (350 to 450.degree. C.) to a lower temperature capable of conducting the unloading work (40 to 50.degree. C.), the catalyst is dumped out in a nitrogen atmosphere by introducing the nitrogen gas into the reactor. Alternatively, a predetermined chemical is added while cooling the catalyst to coat the surface of the catalyst and passivate before unloading the catalyst.
In the aforesaid petroleum refining plant, since the catalyst reacts in a high temperature, the catalyst is agglomerated during the reaction by metal compound, sulfide, coke and other impurities. Thermal conductivity of the agglomerated catalyst is greatly deteriorated and the catalyst is not sufficiently cooled during cooling process. Accordingly, work efficiency for unloading the agglomerated catalyst is lowered, resulting in longer shutdown maintenance term.
In order to facilitate ways dumps out of the agglomerated catalyst, the catalyst is immersed in a surface active agent to soften the agglomerated catalyst.
However, since the waste water after softening the agglomerated catalyst contains compounds contaminating the environment, waste water treatment is necessary. Further, since the catalyst inevitably contacts the air, the dumping process is likely to be dangerous.
Contamination is generated in the process equipment, piping and on a surface of heat-transfer equipment (such as furnace, heat exchanger and stripper) during normal operation in the aforesaid petroleum refining plant.
When the contaminant is generated in piping, for example, the quality of the products deteriorates and production efficiency is lowered since the fluid flow is restricted. In an extreme case, the line may be choked and the devices may be damaged. When the contaminant is generated on the heat-transfer surface, excessive duty is required to the equipment to accelerate deterioration and abrasion of metal and to increase fuel cost.
Therefore, a work for removing the contaminant adhered to the piping and the heat-transfer surface of the process equipment so-called equipment cleaning, is required.
Various chemical cleanings by cleaning fluid are developed as the equipment cleaning.
The chemical cleaning is mainly composed of cleaning process for removing the contaminants from the surface of the equipment and rinsing process for forming clean fluid coat on the surface. In the chemical cleaning, the cleaning fluid is introduced into the equipment and is heated to a predetermined temperature. The heated cleaning fluid is circulated to remove the contaminant from the equipment. Subsequently, water rinsing fluid is used to rinse the equipment.
The aforesaid various methods, i.e., coating the surface of the catalyst to safely unload the catalyst in the air, softening the agglomerated catalyst to easily dump out, and chemical cleaning of the equipment to maintain the operation efficiency of the plant, are developed independently and are conducted as separate processes.
Accordingly, plant shutdown term gets longer, thereby deteriorating the production efficiency.